1. Field of the Invention
This invention relates generally to pressure sensors, and particularly to facedown-type semiconductor pressure sensors for high pressure.
2. Prior Art
FIG. 7 is a sectional view of a conventional facedown-type semiconductor pressure sensor. This semiconductor pressure sensor generally comprises a Si substrate 21 and a pedestal 23. The Si substrate 21 has a thin diaphragm portion 25B which is made by boring the Si substrate 21 from one surface 26, and has an insulating layer 22 on the other surface thereof. Piezoresistive devices are provided in the central region 25A of the insulating layer 22 such that the piezoresistive devices are protected by the insulating layer 22. The other surface of the Si substrate 21 is connected, via the insulating layer 22, to the pedestal 23 having a concave portion 24. Therefore, the opening of the concave portion 24 is closed by the insulating layer 22, and the concave portion 24 operates as a sealed pressure chamber. The concave portion 24 is positioned just under the diaphragm portion 25B such that the side wall 24C of the concave portion 24 is positioned just under the side wall 25C of the diaphragm portion 25B. A pressure which is to be measured is applied to the diaphragm 25B, then pressure difference between the pressure in the sealed pressure chamber 24 and the applied pressure to the diaphragm 25B is detected by the piezoresistive devices.
In the manufacturing process of the above-described conventional pressure sensor, however, the side wall 25C of the diaphragm portion 25B cannot be correctly positioned in accordance with the position of the side wall 24C of the sealed pressure sensor 24. As a result, stress distribution in the diaphragm 25B and in the piezoresistive devices is changed between finished pressure sensors. More specifically, in the conventional facedown-type semiconductor pressure sensors, the connection of the substrate 21 and the pedestal 23 cannot be correctly performed. Therefore, there is a disadvantage that the characteristics of the pressure sensors are not uniformed throughout a number of the products.